Field of the Invention
The invention relates to a catching device for a torn transport belt in a folder of a printing press and to a folder having a catching device.
A catching device of this general type is disclosed in German Published, Non-Prosecuted Patent Application DE 101 06 945 A1. As described therein, the catching device includes a holding device for a transport belt, which has two catching elements between which the transport belt runs and which can hold the latter firmly therebetween, a surface of a first one of the catching elements facing towards the transport belt being convex. The catching device also includes a measuring device for measuring tension of the transport belt, which is constructed so that when the tension falls below a prescribed value, the holding device is triggered.
The transport belt can be part of a transport device for flat products, whether they are signatures or a printing material web, such as for printed copies which are processed in a folder disposed downstream from a planographic printing press or a rotary printing press, in particular a web-fed rotary printing press. In this regard, the transport device can comprise a plurality of such transport belts formed as an endless belt, which are disposed side-by-side and together form the transport surface. However, it can also comprise a single, long endless belt which is guided in such a manner that it forms a plurality of individual strands, respectively, representing one transport belt, the individual strands being disposed beside one another and together forming the transport surface.
In the heretofore-known catching device, the first catching element is a catching roller having a circumferential surface forming the convex surface facing the transport belt. The catching roller is pressed against the transport belt by a pretensioning element and, due to the tension prevailing in the transport belt, is kept at a distance from the second catching element which, in the case of the heretoforeknown catching device, is formed by a locally fixed stop element. This stop element is formed as a round rod which extends transversely to the revolving direction of the transport belt, so that the surface of the second catching element facing the transport belt is also convex.
If the transport belt should then tear upstream of the catching device, as viewed in the revolving direction, the tension of the transport belt collapses thereat and is therefore no longer sufficient to keep the pretensioned catching roller at a distance from the stop element. The catching roller is therefore moved towards the stop element by the pretensioning element and pressed against the stop element, so that the transport belt is clamped therebetween and firmly held. The pretensioning element can therefore be viewed as a measuring device for the tension of the transport belt, because it triggers the holding device when the tension falls below the prescibed value.
One disadvantage of this heretofore-known catching device is that the catching roller and the stop element rest only on a very narrow strip of the transport belt with the convex surfaces thereof facing towards the transport belt, and therefore cannot hold the transport belt sufficiently firmly.
Published European Patent Application EP 0 318 853 A, corresponding to U.S. Pat. No. 4,887,532, discloses a catching device for a torn paper web in a web-fed rotary printing press. Disposed downstream from a printing unit is a clamping and/or severing device for the web, which is formed with a passage slot and is actuatable by a web scanning device that detects a web break. The clamping and/or severing device has clamping jaws and/or knock-off knives which are movable towards one another. However, the precise form of two cooperating clamping jaws cannot be determined from this document.
Published European Patent Application EP 0 476 437 A, corresponding to U.S. Pat. No. 5,163,371, discloses a catching device for a torn printing material web in a web-fed rotary printing press. This heretofore-known catching device has a clamping device disposed downstream from a printing unit and a web break switch. The clamping device comprises a driven roller and a rotor movable by a setting or adjusting device, the printing material web running between the roller and the rotor. The setting device is activatable by the web break switch and then moves the rotor into contact with the roller.
In this heretofore-known catching device, too, the surfaces of the roller and the rotor which face the printing material web are convex.
It is therefore an object of the invention to provide a catching device for a torn transport belt in a folder of a printing press and a folder having a catching device, which can hold the transport belt more firmly than the heretofore-known catching devices and folders of this general type.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a device for catching a torn transport belt. The catching device comprises a holding device for the transport belt, which has two catching elements between which the transport belt runs, the catching elements serving for holding the transport belt firmly therebetween. A first one of the two catching elements has a convex surface facing towards the transport belt, and the second one of the two catching elements has a concave surface facing towards the transport belt. Also provided is a device for measuring tension of the transport belt, the tension measuring device being constructed for triggering the holding device when the tension of the transport belt falls below a prescribed value.
In accordance with another feature of the invention, the first catching element is a roller and the second catching element is a channel, the roller having a rotational axis extending at least approximately parallel to a longitudinal axis of the channel.
In accordance with a further feature of the invention, the channel has a V-shaped cross section.
In accordance with an added feature of the invention, the channel has a circular cross section with an inner diameter at least equal to the diameter of the roller.
In accordance with an additional feature of the invention, in order to hold the transport belt firmly, at least one of the first and the second catching elements is movable towards the respective other of the first and the second catching elements.
In accordance with yet another feature of the invention, the roller is pretensioned against the transport belt.
In accordance with yet a further feature of the invention, the measuring device comprises a pull cylinder having a piston rod to which the roller is affixed, and a housing to which the channel is affixed.
In accordance with yet an added feature of the invention, the measuring device has an end position transmitter disposed at an end of the cylinder housing distal from the channel.
In accordance with yet an additional feature of the invention, the measuring device is constructed for registering a change in speed of a section of the transport belt.
In accordance with still another feature of the invention, the measuring device is constructed for registering speeds of two different sections of the transport belt.
In accordance with still a further feature of the invention, the catching device further comprises at least one further holding device disposed at another location of the transport belt and connected to the measuring device.
In accordance with still an added feature of the invention, the further holding device comprises a clamping block formed with a guide groove wherein the transport belt runs, and a clamping jaw pressed against the base of the guide groove for firmly holding the transport belt.
In accordance with a concomitant aspect of the invention, there is provided a folder disposed downstream of a printing press, as viewed in travel direction of a printing product. The folder includes a device for catching a torn transport belt, which comprises a holding device for the transport belt. The holding device has two catching elements between which the transport belt runs, for holding the transport belt firmly therebetween. A first one of the two catching elements has a convex surface facing towards the transport belt, and the second one of the two catching elements has a concave surface facing towards the transport belt. The catching device further comprises a device for measuring tension of the transport belt, the tension measuring device being constructed for triggering the holding device when the tension of the transport belt falls below a prescribed value.
Thus, the catching device according to the invention is characterized in that that surface of the second catching element which faces the transport belt is concave.
Because the surface of the second catching element is concave, the areas wherein the catching elements rest on the transport belt when they hold it firmly are considerably larger than in the case of the heretoforeknown catching device. The transport belt can therefore be held more firmly.
If the measuring device for the tension is constructed so that the prescribed or predefined tension is virtually zero, then the tension will fall below this value during normal operation only if the transport belt tears. However, the transport belt can also cause undesired disruption if, although it does not tear, it experiences elongation or lengthening due to aging and stress over the course of time. This lengthening or elongation is likewise associated with a reduction in the tension, and the measuring device can also be constructed so that the prescribed tension is greater than the aforementioned very low tension, because typical tension is selected for the tearing. In this case, the measuring device will therefore also trigger the holding device when the maximum permissible lengthening of the transport belt is exceeded.
In addition, when the tension falls below the prescribed value, the measuring device can not only trigger the holding device but also stoppage of the transport belt drive and/or stoppage of the machines associated with the transport belt.
Provision can be made for the first catching element to be a roller and the second catching element a channel, and for the axis of rotation of the roller to extend at least approximately parallel to the longitudinal axis of the channel. In this case, provision can be made in a first alternative for the channel to have a V-shaped cross section, and in a second alternative for the channel to have a circular or U-shaped cross section, the inner diameter of which is equal to or greater than the diameter of the roller. In the case of the first alternative, in order to hold the transport belt firmly, the roller is moved into the channel until the roller is supported on two strip-like areas on the channel, wherein the transport belt is clamped firmly between roller and channel. In the case of the second alternative, the roller can be moved into the channel until it either rests completely on the channel, if the inner diameter of the latter is equal to the diameter of the roller, or rests on a broad strip-like area of the channel, if the inner diameter of the latter is greater than the diameter of the roller.
In addition, provision can be made, in order to hold the transport belt firmly, for the first and/or the second catching element to be moved towards the respective other catching element.
Furthermore, provision can be made for the roller to be pretensioned against the transport belt. As a result, the roller is moved farther towards the channel the greater the extent of decrease in the tension of the transport belt.
Furthermore, provision can be made for the measuring device to have a pull cylinder, to the piston rod of which the roller is fitted, and to the housing of which the channel is fitted. The pull cylinder therefore exerts pretension on the roller in the direction of the channel.
In this case, provision can be made for the measuring device to have an end position transmitter, which is fitted to that end of the cylinder housing which is opposite from the channel end. The end position transmitter will therefore be actuated by the piston of the pull cylinder when that piston has retracted entirely into the housing.
Furthermore, provision can be made for the measuring device to be constructed for registering the change in speed of a section of the transport belt. This is because if the transport belt should tear in the monitored section, the leading end of the transport belt, as viewed in the revolving direction, would experience a positive change in speed, i.e., an acceleration. Therefore, conversely, conclusions about the tearing of the transport belt can be drawn from a sudden acceleration of the monitored section.
Furthermore, provision can be made for the measuring device to be constructed for registering the speeds of at least two different sections of the transport belt. This is because if the transport belt should tear in the monitored section, the speed of this section would differ considerably from that of another section. Therefore, conversely, conclusions about the tearing of the transport belt can be drawn from the difference in speed of two different sections. If the transport device comprises a plurality of such transport belts, which are disposed beside one another and together form the transport surface, the measuring device can register and compare the speeds of the various transport belts, because it is improbable for two monitored transport belts to tear at the same time.
In addition, provision can be made for at least one further holding device also to be disposed at another location of the transport belt and be connected to the measuring device. As a result, the transport belt can be held firmly at a plurality of locations at the same time.
In this case, provision can be made for the further holding device to comprise a clamping block, which has a guide groove wherein the transport belt runs, and a clamping jaw which, to hold the transport belt firmly, is pressed against the base of the guide groove. The guide groove serves for guiding the transport belt during normal operation. In addition, in the event of a tear, it prevents the transport belt from being able to slip out laterally between clamping block and clamping jaw as it is being firmly held.
The catching device according to the invention can be used with particular advantage in a folder which is disposed downstream of a printing press, in particular a web-fed rotary printing press. Typically, a large number of transport belts are used in a folder. It is often the case that not all the locations on the paths formed by the transport belts are easily accessible, so that fixing the transport belt in the event of the tearing of the relevant transport belt maintains at least part of the path. The repair of the old or the installation of a new transport belt is made considerably easier and accelerated. Failure times and downtimes of the folder can be shortened.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a catching device for a torn transport belt in a folder of a printing press and a folder having a catching device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.